1. Field of the Invention
The present invention relates to a steel manufacturing method wherein steel is manufactured by an electric arc furnace using reduced iron pellets as the principal material.
2. Description of the Related Art
As a method for manufacturing steel using reduced iron pellets as the principal raw material, as shown in FIG. 3, charging reduced iron pellets 1 in an electric arc furnace 2 to produce a steel by smelting has been proposed. In this case, because the reduced iron pellets 1 which are the raw material include almost no metal impurities such as Cu, Sn, or Ni, it can be said that there are a superior raw material when the objective is to obtain pure Fe.
In addition, as an applied example of the above method, as shown in FIG. 4, there is also a method wherein scrap 4 is used together with the above reduced iron pellets 1 to manufacture the steel 3. The reason for introducing this scrap 4 is to avoid the disadvantages that the Fe yield decreases, amount of slag produced increases, and the electricity consumption increases due to the melting requiring a long time, because the reduced iron pellets 1 incorporate a large silicon component (SiO2, etc.) and unreduced FeO which forms slag. FIGS. 5.about.7 show how the Fe yield, amount of slag production, and electrical consumption change when the use ratio of reduced iron pellets 1 to the scrap 4 is increased. From these figures, it is clear that when the amount of scrap 4 is large, each of the above problems are ameliorated (FIGS. 5.about.7 are quoted from materials distributed at a conference in Jamshadpur, India, Jan. 11.about.13, 1996, "Alternative Routes to Iron and Steel").
Furthermore, although not a method wherein reduced iron pellets 1 are used as the principal iron component, as shown in FIG. 8, by using the hot metal 6 removed from a blast furnace 5 along with this scrap 4, a steel 3 is produced in an electric arc furnace. This is known as a method which aims at diluting the impurities that accompany melting only scrap 4, shortening the melting time, and lowering electrical power for melting.
However, in the above methods, there are the following types of problems. First, a method for producing steel by using only reduced iron pellets, as has already been described above, cannot be said to be desirable because it entails the problems such as Fe yield decreasing, the amount of slag produced increasing, and electrical power consumption, increasing, etc., due to the existence of silicone components, beginning with the SiO2 included in this reduced iron pellets, and the FeO, etc., which are included at 5.about.10 wt. %.
In addition, when using reduced iron pellets and scrap together, in the smelting of the Cu, Sn, and Ni, etc., in this scrap, elements which cannot be eliminated are included, and thus in the steel produced in the electrical arc furnace, it is impossible to avoid a state where these impurities are mixed in. When these types of impurities are included in the steel, this entails degrading of the product quality, such as impairing the workability of the steel.
Furthermore, when using hot metal derived from the blast furnace and scrap, there is the problem that a blast furnace is necessary to carry this out. However, in providing a new blast furnace, large equipment investment is necessary, and this is not practical. That is, this method can be said to be effective only in a location there a blast furnace is already installed. In addition, even in this method, there is no difference in the above- described use of scrap, and thus even though diluted, the impurities mixed into the steel are in the end a problem.
In consideration of the above- described problems, it is an object of the present invention to provide a steel production method to obtain at a low cost an iron material which is pure and gives superior workability to the produced the steel.